The `target` option expects a string stating the build target when using multi-stage builds.

#### Example: Defining a Build Target for Docker
```yaml
images:
  backend:
    image: john/appbackend
    build:
      docker:
        options:
          target: production
```
**Explanation:**  
The image `backend` would be built using `docker` and the target `production` would be used for building the image as defined in the `Dockerfile`.
